1. Technical Field
The present invention generally relates to fields of display technology and, particularly to a display device, a displaying method, and a driving circuit for a current-driven device.
2. Description of the Related Art
In each pixel of organic light emitting diode (OLED) display devices, charges are generally stored in a capacitor operative with transistors to control brightness of an OLED. The OLED is a kind of current-driven device and can emit lights with different brightness according to values of currents flowing therethrough. Referring to FIG. 1A, showing a circuit diagram of a traditional pixel. The pixel 10 includes a driving circuit 12 and an OLED 16. The driving circuit 12 is for controlling the brightness of the OLED 16 and has a structure of two-transistor-one-capacitor (2T1C). In detail, the driving circuit 12 includes two transistors M1, M2 and a capacitor C1. The transistors M1 and M2 respectively are N-type and P-type. A drain of the transistor M1 is electrically coupled to a data line DL, and a gate of the transistor M1 is controlled by a control signal SCAN to determine whether a data signal on the data line DL is transferred to a source of the transistor M1. A gate of the transistor M2 is electrically coupled to the source of the transistor M1, a source of the transistor M2 is electrically coupled to a power supply voltage OVDD and a drain of the transistor M2 is electrically coupled to an anode of the OLED 16. A cathode of the OLED 16 is electrically coupled to another power supply voltage OVSS. The capacitor C1 is electrically coupled between the gate and the source of the transistor M2.
Referring to FIG. 1B, there is hysteresis effect in the transistor M2. When a gate-source voltage VG of the transistor M2 generated according to a data signal latterly written into the pixel 10 is greater than another gate-source voltage VB of the transistor M2 generated according to another data signal formerly written into the pixel 10, a value of the current flowing through the OLED 16 of the pixel 10 (i.e., generally a drain-source current Ids of the transistor M2) changes from IB (corresponding to a gray scale value such as gray scale 0 of displaying a black image) to IG1, that is, changes along a voltage-current characteristic curve (I-V curve) represented by the “S” shaped dotted line. When the gate-source voltage VG of the transistor M2 generated according to the data signal latterly written into the pixel 10 is less than a gate-source voltage Vw of the transistor M2 generated according to the data signal formerly written into the pixel 10, the value of the current flowing through the OLED 16 of the pixel 10 changes from Iw (corresponding to a gray scale value such as gray scale 255 of displaying a white image) to IG2, that is, changes along a voltage-current characteristic curve (I-V curve) represented by the “S” shaped solid line. In other words, when data signals latterly written into the pixel 10 are the same, currents generated according to the latterly written data signals are different because of the different relative relationships of the data signals latterly written into the pixel 10 and the respective data signals formerly written into the pixel 10, thereby displaying different gray scales. Therefore, as there is hysteresis effect in the transistor of the above-mentioned traditional pixel, an image retention phenomenon may be caused along with the display changing from a high gray scale image to a low gray scale image, thereby affecting the display quality.